The present invention relates to bearings.
It is known that by the rolling action of spherical balls and/or cylindrical rollers in bearings, loads or combinations of loads may be efficiently transmitted from a rotating member to a stationary structure or from one rotating member to another. Bearings containing balls and/or rollers may be configured to accommodate the nature of radial, thrust and moment loads. However, bearings designed to accommodate only pure radial or thrust loads cannot by themselves effectively accommodate a combination of these loads. Moreover, under the influence of moment loading, these bearings are inefficient because they cannot, by themselves, apply a moment reaction to accommodate the moment loading without downgrading the useful life of the bearing.
Angular contact bearings (ball or roller type) can accommodate radial, thrust, and moment loads by using two such bearings either together or separated some distance.
A single row ball bearing using four points of contact at crossed contact angles between the balls and the races can accommodate combinations of radial, thrust and moment loading. The loading imposed on these bearings is very high, and the loading capability of the bearing is reduced, because the highest loaded ball is required to react the combined external loading of radial, thrust and moment loads. Additionally, true rolling of the bearings cannot occur because three or four points of contact between the balls and the race are required to react the combined external loading. This will result in skidding of the balls.
The fatigue life of a ball bearing with point contact at the races is estimated as follows: EQU L=(Q.sub.c /Q).sup.3
where:
L= fatigue life in millions of revolutions; PA1 Q.sub.c = dynamic capacity of the bearing; and PA1 Q= externally applied loads or combination of loads.
The fatigue life of a cylindrical roller bearing with line contact at the races is estimated as follows: EQU L=(Q.sub.c /Q).sup.4
It follows that with a ball bearing and roller bearing of equal dynamic capacity (Q.sub.c), when exposed to the same externally applied load, the roller bearing achieves a longer life. Accordingly, for a ratio of: EQU (Q.sub.c /Q)=3
a ball bearing's estimated life is 27,000,000 revolutions and a roller bearing's estimated life is 81,000,000 revolutions. Thus, the roller bearing achieves three times the life of the ball bearing.